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US 4,433,211 AGranted
Privacy communication system employing time/frequency transformation
AssigneeTechnical Communications Corporation
InventorsArnold M. McCalmont, Matthew W. Slate
Life of this patent
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Abstract
A privacy communication system digitizes a voice signal and divides the signal into different frequency bands or time segments and shifts the bands or segments in frequency and/or time under control of a continually changing pseudo-random key word to develop an encrypted transmitted signal having the same time/bandwidth product as the voice signal.
Claims24
A privacy communication system comprising
- A. means for splitting a voice signal into a selected number of frequency bands;
- B. means for generating a pseudo-random key word;
- C. means for dividing each said band into segments of different time duration in accordance with the pseudo-random key word;
- D. means for compressing said segments in time and expanding them in frequency by a factor equal to the number of frequency bands into which the voice signal was divided;
- and
- E. means for transmitting said time-compressed segments, the transmitted signal having substantially the same time-bandwidth product as the voice signal.
3 more elements
A privacy communication system comprising
- A. means for dividing a voice signal into signal segments;
- B. means for expanding said segments in time and compressing them in frequency;
- C. means for generating a pseudo-random key word;
- D. means for shifting said segments in frequency and in time in accordance with the pseudo-random key word so as to stack said segments so that they span a frequency band which is approximately the same as the bandwidth of the voice signal;
- and
- E. means for transmitting the stacked segments, said transmitted signal having substantially the same time-bandwidth product as the voice signal.
3 more elements
Dependencies are inferred from the claim text.